It has been long accepted practice to treat a variety of vascular disorders in a surgical procedure that involves placement of a tubular endoprosthesis, such as a graft, in a patient's vascular system. The construction and characteristics of the graft typically will be adapted to optimize its use in the specific surgical environment and condition to be treated and, accordingly, a number of different types of grafts are available. Among the most common types of vascular grafts are those formed from a woven or knitted tubular fabric as well as non-fabric tubes such as expanded polytetrafluoroethylene. Such grafts typically are placed in a patient's vascular system in an extensive surgical procedure. In general, the complexity of the surgical procedure required to place the graft will depend on many factors, including the location and surgical accessibility of the portion of the patient's vasculature where the graft is to be placed.
Not all vascular conditions in which it would be desirable to place a graft can be so treated. Among the particularly troublesome medical conditions in which it is desirable to place a graft is that of an abdominal aortic aneurysm, in which a portion of the patient's aorta, the major artery carrying blood from the heart, has developed a weakened wall such that the weakened portion will tend to expand under the influence of the patient's blood pressure. An aortic aneurysm presents a life threatening risk that the aneurysm may burst causing massive internal bleeding. Treatment of the condition typically has involved deeply invasive abdominal surgery in which the patient's abdominal cavity is opened to reach and expose the aortic aneurysm. While maintaining the patient on an independent life support system, the region of the aneurysm is incised lengthwise to enable insertion of the graft into the aorta to span the weakened region and define a structurally tubular flow path between the remaining healthy portions of the aorta. The graft so positioned then is sutured in place. The graft thus serves as a reinforcing liner for the weakened portion of the aorta. Such surgical procedures have been characterized by a relatively high mortality and morbidity rate. Typically, patients suffering from the condition are elderly and are less able to survive the rigors of major abdominal surgery. Additionally, there is a substantial degree of risk when the abdominal cavity is opened because the confining pressure of other abdominal organs on the aorta is released. In some cases, the abdominal wall in the region of the aneurysm is so weak that upon release of the confining pressure, the aneurysm bursts with resulting immediate massive hemorrhaging.
The difficulties and risks associated with the placement of a graft to reinforce an abdominal aortic aneurysm may be reduced significantly by using an endoprosthesis that can be inserted into the patient's blood vessel percutaneously and without requiring extensive surgery. Such devices, and delivery systems for their percutaneous placement are disclosed in the above-identified U.S. patent applications. Those devices include an endoprosthesis having an elongate flexible tubular graft attached to one or more anchors that support the flexible graft and serve to retain the graft in the deployed location in the blood vessel with reduced risk of the graft migrating from its deployed position. The anchor(s) is radially contractible and expandable between a reduced diameter, low profile configuration in which it can be inserted percutaneously into the patient's blood vessel and an expanded configuration in which the anchor(s) is deployed in the blood vessel and engages the inner luminal surface of the blood vessel sufficiently and in a manner to reduce the risk of the graft assembly migrating from its deployed location. In order to further reduce the risk of migration, the device may be provided with one or more hooks that can engage the wall of the blood vessel when the anchor is expanded. Although the use of such hooks is considered to be highly desirable, they may present some difficulty when the device is contracted to a deliverable configuration. The hooks which should extend radially outwardly, may become caught on a portion of the delivery device or may become caught with each other as the device is radially contracted. That may present difficulty when the device is deployed in the patient's blood vessel. Should any of the hooks become caught, that may impair the ability of the device to be properly expanded and may interfere with the ability of the device to be positioned initially or repositioned by the delivery device.
As described in the above-identified pending patent applications, the delivery system includes an elongate, flexible catheter-like device having a tubular sheath at its distal end (the end inserted into the patient). When the endoprosthesis is contracted radially, it can be contained within the sheath of the delivery device. The delivery device then is inserted into the patient either percutaneously or by surgical access and is navigated to the intended placement site. The endoprosthesis then can be ejected from the sheath and can expand to its deployed configuration. As described in further detail in pending application Ser. No. 08/147,498, the device may be only partially ejected from the delivery sheath to permit the physician to verify that the endoprosthesis is in its intended position. If so, the endoprosthesis can be fully released. If not, the endoprosthesis can be withdrawn into the sheath, the sheath can be repositioned, and the endoprosthesis can be again released at the intended location or totally removed from the patient.
It would be desirable, therefore, to provide an endoprosthesis and delivery system therefor that provides the advantages of using hooks to securely engage the blood vessel wall but in which the hooks can be easily disengaged from and reengaged with the blood vessel wall and with reduced risk of the hooks becoming entangled themselves or with other portions of the device and without hindering the deployment and repositioning of the endoprosthesis. It is among the general objects of the invention to provide such a devices and technique for their use.